<!DOCTYPE html>
<html>
	<head>
		<meta charset="utf-8">
		<title>calc函数</title>
		<style type="text/css">
			.father {
				width: 300px;
				height: 200px;
				background-color: #00FF00;
			}

			.son {
				width: calc(100% - 30px);
				height: calc(100% - 30px);
				background-color: #0000FF;
			}
		</style>
	</head>
	<body>
		<!-- 让子盒子永远比小盒子小30px -->
		<div class="father">
			<div class="son"></div>
		</div>
	</body>
</html>
